Fuel injection valve for high-pressure injection with improved control of fuel delivery

ABSTRACT

A fuel injection valve for high-pressure injection of fuel from a high-pressure reservoir into a combustion chamber of an internal combustion engine, especially a diesel engine, is described. The fuel injection valve has a magnet valve by means of which the fuel pressure can be either relieved (injection position) or built up (closing position) in a control chamber via a throttle having at least one throttle conduit segment defined by conduit walls. According to the invention, the throttle conduit segment is embodied substantially in the form of a variable aperture, or a variable throttle aperture.

PRIOR ART

The invention relates to a fuel injection valve for high-pressureinjection of fuel from the high-pressure reservoir into a combustionchamber of an internal combustion engine as generically defined by thepreamble to claim 1.

One such fuel injection valve is described in German Patent DisclosureDE 196 19 523 A1. In this known injection valve, the control of theinjection is effected electrohydraulically, by delivering fuel from thehigh-pressure reservoir at high pressure to a control chamber. By meansof this control pressure, the valve member of the fuel injection valveis then kept in the opening position. This is attained because thecontrol surface area of the valve member acted upon by the controlpressure is greater than the area acted upon of the shoulder of thenozzle needle of the fuel injection valve. The control chambercommunicates permanently with the high-pressure reservoir, specificallyin throttled fashion, and it can be relieved via a further throttle witha throttle conduit segment. This latter throttle is controlled by amagnet valve. As soon as the magnet valve opens this throttle, thecontrol chamber is relieved, and as a result the pressure at thepressure faces of the valve member of the injection valve is sufficientto allow it to be put into the open position or in other words theinjection position, during which the injection takes place. If thisthrottle is now closed again by the magnet valve, an increase ofpressure occurs in the control chamber, and as a consequence the valvemember is returned to the opening position. The fuel injection valvealso has a relief line, leading away from the electromagnet of themagnet valve, and the fuel quantity diverted at the aforementionedthrottle can flow out to a relief chamber via this line.

A similar basic layout is also described in European Patent DisclosureEP 0 661 442 A1. The throttle, which is controllable by means of themagnet valve and which seals off the side of the fuel injection valvetoward the relief line or opens it and connects it with the controlchamber, has two cylindrically embodied conduit portions. The firstconduit portion, which represents the actual throttle conduit crosssection, is relatively long compared to its diameter and discharges withan abrupt change in cross section into the second cylindrical portion,which has a considerably larger cross section and establishes thecommunication between the actually thin, long throttle conduit segmentand the control chamber.

Especially in the case of the slender, long and thin throttle conduitsegments, the flow of fuel has enough time to develop in such a way thatthe fuel presses against the conduit walls. With such narrow throttleconduit cross sections, however, this entails not inconsiderable flowlosses. To reduce the flow losses, the course taken is to lap theconduit walls of these throttle conduit cross sections in order toreduce their roughness. This involves major technological effort,however, which means high production costs. Particularly with verynarrow throttle conduit cross sections, this kind of superfine surfacemachining runs up against the limits of technical feasibility, takingreasonable costs into account.

The object of the invention is therefore to create a fuel injectionvalve whose throttle between the magnet valve and control chamber can bemanufactured at little production effort or expense and with low flowlosses.

This object is attained with a fuel injection valve is having thecharacteristics of claim 1. Expedient refinements are defined by thedependent claims.

ADVANTAGES OF THE INVENTION

The fuel injection valve according to the invention for thehigh-pressure injection of fuel from a high-pressure reservoir into acombustion chamber of an internal combustion engine, specifically adiesel engine, has a magnet valve by means of which the fuel pressure ina control chamber, via a throttle which has at least one throttleconduit segment with conduit walls, can be relieved, which correspondsto the injection position of the fuel injection valve, or built up,which corresponds to the opening position of the fuel injection valve,or the noninjection position. According to the invention, the throttleconduit segment is embodied substantially in the form of a variableaperture. Because the throttle conduit segment is embodied as a variablethrottle aperture, an intentional influence is exerted on thedevelopment of the flow in the throttle conduit cross section, by makingthe actual throttle conduit segment so short that in its action it islike a variable aperture, in which when there is a flow to it, theconduit portions preceding the variable aperture and the fuel injectionvalves downstream of the variable aperture are substantially untouchedby the flow at their conduit walls. This creates less flow resistance,on the one hand, so that the control behavior of the fuel injectionvalve can be improved considerably. On the other, because the throttleconduit cross section is embodied as a variable aperture, thecomplicated and expensive superfine surface machining in the otherwiserelatively narrow flow conduit is dispensed with. As a result, theproduction costs can be reduced. Moreover, this reduces the influence ofthe precision of production on the flow behavior in such a throttle,since the flow through the immediate region of the throttle issubstantially independent of the form of the surface of the remainder ofthe conduit.

The throttle conduit segment preferably has an l/d ratio such thatcavitation occurs intentionally. Via a special geometric embodiment,especially a short length, it is also attained in this exemplaryembodiment that the flow, when there is a flow through the actualthrottle conduit segment, substantially does not press against itsconduit walls, thus reducing the flow losses.

Preferably, the throttle conduit segment has an l/d ratio in the rangefrom 0.1 to ≦2, in particular 1.0 to 1.5. In this connection, it can benoted that in particular in accordance with theoretical tests with l/dratios in the range from 2 to 3, no cavitation occurs. In a practicalsense, however, the cavitation does occur but is reduced. To preservethe original effect, namely to employ cavitation intentionally so thatthe flow will not press against the conduit wall, the length of thethrottle conduit segment in proportion to its diameter is reducedconsiderably, thus achieving greatly reduced l/d ratios. Especially atvery low l/d ratios, the throttle conduit segment assumes the form of avariable throttle aperture.

To exert a further purposeful influence on flow conditions inside thethrottle, in a further preferred feature of the invention, the throttleconduit segment is embodied in a transition region with cross-sectionalenlargement in the direction toward the control chamber in roundedfashion, in particular HE-rounded. Because of the rounded embodiment ofthe transitional region, the constriction of the fuel stream is reduced,which further reduces flow losses in the flow through the actualthrottle conduit cross section or variable throttle aperture.

Preferably, the throttle has a first throttle conduit, which is closableby means of a closing element of the magnet valve, and a second throttleconduit, which discharges into the control chamber, and the variableaperture-like throttle conduit segment or variable throttle aperture isdisposed between the first throttle conduit and the second throttleconduit in an approximately axial direction to one another. Thediameters of the throttle conduits are embodied such that flow lossesare kept relatively low, and the variable aperture like throttle conduitsegment between the two throttle conduits is made so short that it takeson the form of a variable throttle aperture.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Further advantages, characteristics and possible applications of theinvention will now be described in detail in terms of an example inconjunction with the accompanying drawings. Shown are:

FIG. 1, a cross-sectional view of a fuel injection valve forhigh-pressure injection to explain its basic functioning;

FIG. 2, an enlarged sectional view of the region of the fuel injectionvalve of FIG. 1, in which the throttle is disposed along with thevariable aperture-like throttle conduit segment according to theinvention.

In FIG. 1, a longitudinal section is shown through a fuel injectionvalve for high-pressure injection of fuel with a magnet valve 2integrated with it. The valve housing 17 of the fuel injection valveincludes a bore into which a nozzle needle 11 is provided, the nozzleneedle having a conical sealing face known per se, which in the closingstate comes into contact with a conical valve seat. Extending away fromthis valve seat are injection bores, which represent the actual nozzle13 in the nozzle body 12. The nozzle needle 11 is urged in the closingposition onto the valve seat by a compression spring 16. The nozzleneedle 11 also has a pressure shoulder 15, in the vicinity of which apressure chamber 14 is provided in the nozzle body 12; this chambercommunicates with a high-pressure inlet line 26, by way of which fuel isdelivered at high pressure, preferably a pressure of 120 MPa to thepressure chamber 14 from a high-pressure connection 18 in the form of apressure neck. When the appropriate high pressure prevails in thepressure chamber 14, it acts on the pressure shoulder 15 and thusgenerates a force acting in the axial direction of the nozzle needle 11;given suitable control of the magnet valve 2, this force is sufficientto lift the nozzle needle 11 and uncover the nozzle bores of the nozzle13 in the nozzle body 12. As a result, fuel is injected into thecombustion chamber of the engine. In coaxial alignment with thecompression spring 16, a valve tappet 25 also engages the nozzle needle11; with its end face, this tappet defines a control chamber 3 in aninsert part 21 in the valve housing 17 of the fuel injection valve 1.This control chamber 3, from the high-pressure connection 18, has aninlet with a high-pressure throttle 19 and an outlet to a relief line 24that has the throttle 4 according to the invention, which is controlledby a valve member 27 of the magnet valve 2.

In a manner known per se, the magnet valve 2 has a spring 20 acting inthe opening position and a magnet coil 22, which when excited attractsthe valve member 27, thus opening the throttle 4. In the upper headregion of the fuel injection valve 1, an electrical connection 23 isprovided for supplying current to the magnet valve 2.

For the sake of clearer illustration, the region of the throttle 4 ofthe invention is shown again in FIG. 2 as an enlarged sectional view.The throttle 4 has a first throttle conduit 8, which is closable bymeans of a ball-like closing element 9 that is actuatable by the magnetvalve 2; a throttle conduit segment 5, which includes a roundedtransitional region 6 is embodied in the form of a variable aperture;and a second throttle conduit 10. The transition of the throttle conduitportion 5 is embodied as the rounded transitional region 6, tocounteract constriction of the fuel stream. The second throttle conduit10 discharges into the control chamber 3, in which the valve tappet 25is located that can be acted upon by fuel pressure through suitablepressure in the control chamber 3. The magnet valve-controlled throttle4 according to the invention is disposed inside the valve housing 17.

Because the throttle conduit segment 5 has such a short length or an l/dratio such that it acts as a variable throttle aperture, and because thetransitional region from this throttle conduit segment 5 to the secondthrottle conduit 10 is embodied as a rounded transitional region 6, andbecause the geometric relationships among the individual throttleconduits or throttle conduit segments and the radii of the roundedtransitional region 6 are adapted to one another, the embodiment of theflow through the throttle can be optimized along all the conduitportions or throttle conduits with a view to optimal control of the fuelinjection valve 1.

The foregoing relates to a preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A fuel injection valve (1) for high-pressureinjection of fuel from a high-pressure reservoir into a combustionchamber of an internal combustion engine which has a magnet valve (2) bymeans of which the fuel pressure selectively can be either relieved in afirst injection position or built up in a second closing position in acontrol chamber (3) via a throttle (4) having at least one throttleconduit segment (5) defined by conduit walls, and the throttle conduitsegment (5) is embodied with a rounded transitional region (6) in theform of a variable aperture, and the throttle conduit segment (5) has alength to diameter (l/d) ratio chosen to cause cavitation thereof, and ageometric embodiment, in particular a length thereof, such that during aflow of fuel through said segment, the flow substantially does not pressagainst the conduit walls.
 2. The fuel injection valve (1) according toclaim 1, in which the throttle conduit segment (5) has an l/d ratio in arange from 0.1 to ≦2.
 3. The fuel injection valve (1) according to claim1, in which the throttle conduit segment (5) is embodied in a transitionregion (6) with a cross-sectional enlargement in rounded fashion asviewed in a direction toward the control chamber.
 4. The fuel injectionvalve (1) according to claim 2, in which the throttle conduit segment(5) is embodied in a transition region (6) with a cross-sectionalenlargement in rounded fashion as viewed in a direction toward thecontrol chamber.
 5. The fuel injection valve (1) according to claim 1,in which the throttle (4) has a first throttle conduit (8), which isclosable by means of a closing element (9) of the magnet valve (2), anda second throttle conduit (10), which discharges into the controlchamber (3), and the throttle conduit segment (5) is disposed betweenthe first throttle conduit (8) and the second throttle conduit (10) inan approximately axial direction to one another.
 6. The fuel injectionvalve (1) according to claim 2, in which the throttle (4) has a firstthrottle conduit (8), which is closable by means of a closing element(9) of the magnet valve (2), and a second throttle conduit (10), whichdischarges into the control chamber (3), and the throttle conduitsegment (5) is disposed between the first throttle conduit (8) and thesecond throttle conduit (10) in an approximately axial direction to oneanother.
 7. The fuel injection valve (1) according to claim 3, in whichthe throttle (4) has a first throttle conduit (8), which is closable bymeans of a closing element (9) of the magnet valve (2), and a secondthrottle conduit (10), which discharges into the control chamber (3),and the throttle conduit segment (5) is disposed between the firstthrottle conduit (8) and the second throttle conduit (10) in anapproximately axial direction to one another.
 8. The fuel injectionvalve (1) according to claim 4, in which the throttle (4) has a firstthrottle conduit (8), which is closable by means of a closing element(9) of the magnet valve (2), and a second throttle conduit (10), whichdischarges into the control chamber (3), and the throttle conduitsegment (5) is disposed between the first throttle conduit (8) and thesecond throttle conduit (10) in an approximately axial direction to oneanother.
 9. The fuel injection valve (1) according to claim 1, in whichthe throttle conduit segment (5) has an l/d ratio in a range from 1.0 to1.5.